A large number of amplifier circuits are known in the art. Amplifier circuits are used for many different applications with many different requirements, for example in terms of electrical requirements/constraints: input level, output level, power consumption, heat dissipation, power efficiency, signal bandwidth, signal distortion, noise level, group delay, but also in terms of component cost, PCB size, etc.
Typically several requirements may conflict each other, and thus typically a trade-off needs to be made. There is no single ideal circuit topology which is best for all applications, but each type or class of amplifier has its own advantages and disadvantages.
The present invention is related to a new class of amplifier circuits with a high level of integration (in a semiconductor device), which is suitable for amplifying or pre-amplifying relatively small signals (e.g. having an amplitude less than 1 mV or even less than 100 μV) and provides good noise characteristics by incorporating chopper modulation (to avoid increased noise levels due to offset and flicker noise).
It is well known in the art, for example from C. Enz and G. C. Temes; “Circuit techniques for reducing the effects of op-amp imperfections: autozeroing, correlated double sampling, and chopper stabilization,” Proc. IEEE, Vol. 84, No. 11, pp. 1584-1614, November 1996, further referred to herein as [Enz96], that chopping can be used to eliminating offset and flicker noise.
FIG. 1 shows an amplifier circuit presented by Q. Fan, J. H. Huij sing, and K A. A. Makinwa, “A 21 nV/sqrtHz chopper-stabilized multipath current-feedback instrumentation amplifier with 2 μV offset”, IEEE ISSCC. Dig. Tech. Papers, pp. 80-81, February 2010. The circuit contains three choppers CH1, CH2, CH3, two transconductances Gin, Gfb, a current integrator Gint with an integrating capacitor Cint, and two resistors R1, R2 arranged as a voltage divider. The circuit transfer has an overall first order response (a single dominant pole).
There is always room for improvements or alternatives.